Clothing provides protection from the sun by the fabric blocking, scattering and/or absorbing harmful radiation. A long sleeve shirt and long pants give protection to arms and legs, and collared shirts somewhat protect the neck.
In hot conditions, it’s wise to choose materials that are lightweight, loose and can breathe easily to prevent overheating, but this goes against common thinking that thicker materials provide better UV protection.
Clothing with denser fabrics such as cotton, linen, hemp, polyester, nylon, spandex and polypropylene are more effective at blocking, scattering and/or absorbing harmful radiation. Health organisations recommend them. A study suggests that a simple see-through test is not a valid test of UV penetration. The reason is that in some materials visible light is scattered, but UV can still penetrate. The human eye cannot see UV, so even if all visible light is blocked, UV can still penetrate. Hence visible light transmission is not a reliable test of UV transmission.
Originally, clothing was given an SPF standard based on a measure of how long it takes for a person’s skin to burn under the material. More recently, UPF ratings were introduced giving an indication of how well a piece of fabric can block UV. UPF are now considered a more reliable measure of a fabric’s protection against UV since different skin types burn at different rates.
In practical terms, most day-to-day clothing provides moderate sun protection. A study of typical clothing worn by the general public found that around three-quarters of clothing types regularly worn would offer protection of more than SPF 15. However, for bushwalking, where sun exposure is generally higher, it may be worth considering clothing that has a certified UPF rating, which is the measure of UVA/UVB penetration for fabrics. Old or worn fabric is less likely to protect from UV.
Clothing with UPF ratings are specially manufactured materials to absorb harmful radiation. One way of doing this is to embed the material with nanoparticles that absorb the appropriate wavelengths of light. Counter-intuitively, studies have shown that washing appears to improve UV qualities of clothing perhaps due to the shrinking effect or because of the chemicals in washing powders. Companies now manufacture laundry products so that consumers can ‘wash’ UV protection into their clothing.
As assessing the UV index on a walk may be difficult if not impossible, a simple solution is to act as if the sun is very strong. This could mean wearing a broad brim hat with a flap at the back, a long sleeve shirt and sunscreen on most walks. People who burn easily could also wear long pants and light gloves. A cloth barrier may and often does work better than sunscreen because clothing can’t rub or sweat off and the wearer often doesn’t need to remember to put clothes on every two hours. Essentially, the more protective clothing the user wears, the need for sunscreen decreases.
To summarise, clothing may provide an effective barrier to harmful radiation from the sun. Avoid torn, old or worn clothing, and consider using materials that have certified UPF ratings.